1. Field of the Invention
The present invention relates to a data processing system with a dynamic address translation function for translating a virtual address into a real address and for processing data, and particularly, to a data processing system with a dynamic address translation function that secures data from destruction.
As the number of users of computer systems and the importance to society of computers increases, protecting computer systems and user data is becoming more important.
2. Description of the Related Art
A computer system with a channel unit having a conventional dynamic address translation function to control input/output units will be explained.
The computer system provides users with virtual data spaces, respectively. If it provides each user with a real address, the user may access an area in a main memory of the system. Then, there will be a risk of the user unknowingly destroying data in a system area or data in other user areas in the memory. To avoid the risk, the users are provided with the respective virtual spaces and are allowed to access the main memory only through the virtual spaces.
When transferring data between the main memory and the input/output units, the channel unit translates a virtual address related to the data into a real address by the use of a single control register. The register holds an address that specifies a segment table, which is used to translate the virtual address into the real address.
This prior art uses the control register to translate virtual addresses related to not only a channel program but also user data into real addresses. Namely, a user space where the user data are developed is not independent of a system space where the channel program is developed, and therefore, each user can access the channel program in the system space, to sometimes destroy data in the system space without knowing it.